Abiotic Input of Fixed Nitrogen by Bolide Impacts to Gale Crater During the Hesperian: Insights From the Mars Science Laboratory

Abstract

Molecular hydrogen (H2) from volcanic emissions is suggested to warm the Martian surface when carbon dioxide (CO2) levels dropped from the Noachian (4100 to 3700 Myr) to the Hesperian (3700 to 3000 Myr). Its presence is expected to shift the conversion of molecular nitrogen (N2) into different forms of fixed nitrogen (N). Here we present experimental data and theoretical calculations that investigate the efficiency of nitrogen fixation by bolide impacts in CO2‐N2 atmospheres with or without H2. Surprisingly, nitric oxide (NO) was produced more efficiently in 20% H2 in spite of being a reducing agent and not likely to increase the rate of nitrogen oxidation. Nevertheless, its presence led to a faster cooling of the shock wave raising the freeze‐out temperature of NO resulting in an enhanced yield. We estimate that the nitrogen fixation rate by bolide impacts varied from 7 × 10−4 to 2 × 10−3 g N·Myr−1·cm−2 and could imply fluvial concentration to explain the nitrogen (1.4 ± 0.7 g N·Myr−1·cm−2) detected as nitrite (NO2−) and nitrate (NO3−) by Curiosity at Yellowknife Bay. One possible explanation is that the nitrogen detected in the lacustrine sediments at Gale was deposited entirely on the crater's surface and was subsequently dissolved and transported by superficial and ground waters to the lake during favorable wet climatic conditions. The nitrogen content sharply decreases in younger sediments of the Murray formation suggesting a decline of H2 in the atmosphere and the rise of oxidizing conditions causing a shortage in the supply to putative microbial life.

Constraints on the Mineralogy and Geochemistry of Vera Rubin Ridge, Gale Crater, Mars, From Mars Science Laboratory Sample Analysis at Mars Evolved Gas Analyses

“…Conversely, higher in the stratigraphy NO was either not evolved or evolved at very low levels indicating either very low abundances or a lack of nitrate/nitrite salts (or other N sources for the N in NO)-until RH. The temperature of the NO peak in RH is most consistent with the temperature of NO evolution from Fe nitrate, Fe nitrite, or Fe nitrate/nitrite mixed with an oxychlorine salt, under SAM-like conditions in the lab (Navarro-González et al, 2019;Stern et al, 2015). As for the oxychlorine salts in RH, the presence of likely nitrate/nitrite salts in RH and not in DU, ST, HF, or the previous samples OU and above can inform possible fluid interactions recorded in the samples, and this is discussed further in section 5.…”

Nitrates as a Potential N Supply for Microbial Ecosystems in a Hyperarid Mars Analog System

“…Our results from Atacama soils suggest that potentially extant Martian life could survive under the high levels of nitrate availability [3,33,34]. On Mars, the concentrations of nitrate and TOC should be even more tightly regulated by local sedimentation rates after the early Martian periods dominated by impact thermal shocks [40][41][42], since the more recent dry Mars does not have detectable rainfall. With the equilibrium between Martian nitrate and atmospheric nitrogen stabilized by impact thermal shocks and without rainwater to leach nitrate away, the nitrate availability near the surface on the more recent dry Mars remains nearly unchanged.…”

“…The transitional and arid sites, on the other 40 hand (sites TZ-4, TZ-5 and TZ-6), are more analogous to regions of Mars where precipitation and 41 organic C levels might have been slightly elevated, like Noachian Mars [67]. Therefore, comparisons 42 between the hyperarid sites and transitional/arid sites provide insight into the strategies that 43 potentially extant microorganisms on Mars might have uses to respond to changes in rainwater and 44 nitrogen input. 45 Nitrate concentrations in our samples do not directly scale with precipitation estimates, as might 46 be expected ( Figure 3).…”

“…Some Martian nitrate could also originate from carbon dioxide-nitrogen reactions in the ancient Martian atmosphere stimulated by impact shock heating [39,40]. Thermal decomposition triggered by the late heavy bombardment could also have reversely converted Martian nitrate back to atmospheric nitrogen, redistributing the sedimentary nitrate content and balancing the equilibrium between nitrate and atmospheric nitrogen [41,42].High levels of nitrate that build up under hyperarid conditions, like the Atacama Desert and the recent Martian surface, could potentially provide the dominant source of bioavailable N for local microbial communities in the subsurface. Nitrate is a significant N source for a variety of microorganisms [43].…”

“…Some Martian nitrate could also originate from carbon dioxide-nitrogen reactions in the ancient Martian atmosphere stimulated by impact shock heating [39,40]. Thermal decomposition triggered by the late heavy bombardment could also have reversely converted Martian nitrate back to atmospheric nitrogen, redistributing the sedimentary nitrate content and balancing the equilibrium between nitrate and atmospheric nitrogen [41,42].…”